The present invention relates to a woven fabric for paper-making. Conventionally, there are many requirements for woven fabrics for paper-making. The requirements include, for example:
(1) Prevention of wire marks formation and improvement of paper-making retention by enhancing the surface smoothness and improvement of a stock's property for supporting fiber; PA1 (2) Extension of service life of woven fabric and improvement of running property by enhancing the abrasion resistance; and PA1 (3) Improvement of stiffness, stable attitude and dimension stability, excellent water drainage; and ensuring low water holding property. These requirements are correlated mutually and, in principle, the properties are not independent. However, roughly speaking, the requirement (1) relates mainly to the paper-making face side of woven fabric; the requirement (2) relates mainly to the running face side of woven fabric; and the requirement (3) relates mainly to the whole structure of woven fabric.
Many proposals have been made heretofore for responding to the mentioned requirements. However, satisfactory methods have not been found yet. For example, fine weaving using fine yarn might be a solution for settling the requirement (1) to form a smooth paper-making face; however, such woven fabric is unsatisfactory for abrasion resistance of requirement (2) and stiffness and stable attitude of requirement (3).
Recently, some trials for improving a stock's property for supporting fiber have been made from the standpoint of fabric structure including forming the paper-making face with wefts. The formation of the paper-making face with wefts improves water drainage as well since the water drainage space existing among warps is not blocked by the fibers of the stock. More specifically, for example, auxiliary wefts are placed adjacent to the original wefts. This method has been practiced for single and double woven fabrics; however, the results cannot be said to be sufficiently satisfactory.
On the other hand, as for the enhancement of abrasion resistance requirement (2), the prevention of wear of warps has been practiced conventionally as a type of weft abrasion in which the running face of the paper-making woven fabric is formed by wefts. Generally, the function of wear-resistance is preferred to be borne by the wefts in view of extension of the service life of a woven fabric in use, attitude (shape) and dimensional stability as well. When the warp is worn, it is a matter of course that the tensile strength is lowered and the dimension of the woven fabric is elongated. When the abrasion continues, the woven fabric cannot bear the tension and then breaks and the service life is over. From the standpoint of yarn material, polyamide yarn is used for the running face side yarn since polyamide yarn is more wear-resistant than polyester. However, this is just a matter of material performance and cannot bring about a drastic effect. Use of polyamide yarn, on the other hand, is disadvantageous in that the stiffness and stable attitude of the requirement (3) are deteriorated. Thus, polyamide yarn and polyester yarn are use alternatively at most.
Trials to use yarn of large diameter for the running face weft have been made and some improvement has been made thereby. However, the balance between the weft and warp cannot be kept, and crimping property is worsened. As a result, the prevention of wire marks of the requirement (1) cannot be realized. Hence, the trials have been problematic in practice.
As explained above, the requirements (1) through (3) are contradictory in some aspects. For example, a trial to overcome the requirement (1) contradicts the requirement (2). In this regard, trials to overcome these problems with upper and lower two layered woven fabric have been made in which different warps and different wefts are used in the paper-making face side and running face side respectively, and the woven fabrics of both layers are integrated by binding yarn. That is, the paper-making face is formed by using warp and weft of smaller size to make the paper-making face side woven fabric smooth, and the running face is formed by using warp and weft of larger size to make the running face of greater wear-resistance.
However, the results have not been completely satisfactory. That is, the binding yarn pulls the woven fabric at the paper-making face side into the running face side at the connection part where the binding yarn crosses the warp or weft, and concave parts are generated on the woven fabric surface at the paper-making face side. The concave parts cause wire marks as if transcribing on to a sheet of paper. More recently, trials to improve the wear-resistance, in double weft woven fabric, have been made by enlarging the wear-resistant volume. In that case, shafts of 14 or 16, which are twice as large as usual shafts, are used, and crimps twice as long as the usual ones are formed in the lower weft. The results are good. However, still there remains unsatisfactory performance in many respects including the surface smoothness of the requirement (1) and stiffness and water holding property of the requirement (3).
The solution for the requirement (2) for paper-making woven fabric is now very important since the need for high speed paper-making, increased filler amount, and neutral paper is becoming more urgent. In addition, even though use of paper-making woven fabric of multiple weave has increased and high speed paper-making has progressed, these have brought new problems. Woven fabric of multiple weave attains stiffness, stable attitude, and wear-resistance that cannot be realized by single layer woven fabric; however, its structure makes the water holding increased. Thus, water contained in the woven fabric is sprayed as water drops at the returning part by centrifugal force with high speed rotation, and the water drops fall on wet paper causing marks on the paper.
Paper-making woven fabrics of single weave do not cause such a problem since they retain small amount of water. However, conventional paper-making woven fabrics of single weave normally form the running face having long crimps of weft for the purpose of maintaining wear-resistance. Hence, long crimps of warp are placed in parallel in the paper-making face side in a paper-making woven fabric of single weave; knuckles of the weft protrude therebetween. When paper stock is fed to a running paper-making woven fabric, the stock fibers are oriented inevitably to the running direction and deposited among the long crimps of warp. When the fibers are blocked, the space for filtrate water passes is blocked. Since the filtrate water is blocked in this way, more vacuum is required for dehydrating for the compensation; as a result wire marks are formed.